algorithm.cpp failed with clang-cl on Windows for "declaration does not declare anything"

With the latest version of clang-cl, algorithm.cpp get failed with clang-cl on Windows for "declaration does not declare anything".
Related code:
https://github.com/boostorg/range/blob/72e2a4457a13eba0b8cddd2e68f058f74bd3d890/test/algorithm.cpp#L32-L35
A small reproducer(test.cpp):
```
namespace boost {
template
class counting_iterator
{};
}
template ::boost::counting_iterator;
```
Error message:
```
ksh-3.2$ clang-cl -c test.cpp
test.cpp(6,10): error: declaration does not declare anything
template ::boost::counting_iterator;
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.
```
The code is considered as not accepted(https://github.com/llvm/llvm-project/commit/1cbdf932b41eb58ed94fbc240e93b63653d95bd3).